1. Field of the Invention
The present invention generally pertains to an integrated facility for the co-production of ethanol and biodiesel fuel. In particular, corn oil isolated from the whole stillage of a corn ethanol distillation process is utilized as a feedstock for a biodiesel plant, along with alcohol (e.g., methyl alcohol, ethyl alcohol, and mixtures thereof), operating within the same general facility as the corn ethanol plant. By-products of the biodiesel plant, such as liquid crude glycerol and gaseous or liquid alcohols, can be utilized in various parts of the ethanol plant thereby increase the operating efficiency thereof.
2. Description of the Prior Art
Corn oil is a by-product of a corn ethanol production. The corn oil is generally carried through the fermentation and distillation portions of a corn ethanol plant into the whole stillage that is removed from the distillation system. The whole stillage is commonly separated into a thin stillage, which includes the corn oil, and a cake that can be dried to produce dried distillers grains with solubles (DDGS), which can be used as an animal feed. The thin stillage can be processed to remove moisture therefrom and form nutritive syrup that can also be used as an animal feed material. Alternatively, the corn oil may be extracted from the thin stillage and be made a saleable product.
The corn oil extracted from the thin stillage has many industrial uses, such as in soaps, paints, rustproofing materials, inks, textiles, and insecticides. Corn oil can also be used as a feedstock in the production of alternative fuels such as biodiesel and renewable diesel. Biodiesel refers to a vegetable oil- or animal fat-based diesel fuel comprising long-chain alkyl (methyl, ethyl, or propyl) esters. Biodiesel is generally not considered to be a full replacement of conventional petrodiesel for use in most diesel engines. Rather, it is generally blended with petrodiesel for use in the retail diesel fuel marketplace. Renewable diesel, on the other hand, is produced by hydrotreatment of corn oil, for example, resulting in a hydrocarbon fuel that is very similar to petroleum diesel in its chemical composition.
A number of reaction schemes exist for conversion of corn oil into renewable diesel. Hydrotreating is one such process in which the corn oil feedstock is reacted with hydrogen under elevated temperature and pressure to change the chemical composition of the feedstock. In the case of renewable diesel, hydrogen is introduced to the feedstock in the presence of a catalyst convert the triglyceride molecules into paraffinic hydrocarbons. In addition to creating a fuel that is very similar to petrodiesel, this process creates other hydrocarbon by-products including lower hydrocarbon fuel gas compounds (e.g., methane, ethane, propane, and butane) and higher hydrocarbon naphtha.
Production of biodiesel usually involves using corn oil and alcohol as feedstocks to a biodiesel reactor where the corn oil first undergoes an acid esterification reaction whereby the free fatty acids are converted to an alkyl ester through the introduction of a strong acid (e.g., sulfuric acid). The triglycerides are then subjected to a base-catalyzed reaction in the presence of strong base (e.g., KOH) and the alcohol feedstock, in order to form alkyl esters. The ester reaction product is then separated from the glycerol fraction which also contained excess alcohol used in the transesterification reaction.
Generally, the corn oil and/or alcohol feedstocks are produced at a plant location remote from the biodiesel facility, thus requiring transport of these feedstocks via pipeline, railway tankers, or tanker trucks. This added transportation cost increases the overall expense in the manufacture of biodiesel and decreases its competitiveness with petrodiesel as an alternative fuel source.
The following references describe various types of ethanol and biodiesel production methods: U.S. Pat. No. 6,927,048, U.S. Pat. No. 7,608,729, U.S. Pat. No. 7,649,086, U.S. Pat. No. 8,152,867, U.S. Pat. No. 8,227,015, U.S. Pat. No. 8,454,802, US2008/0176298, US2009/0017164, US2009/0311374, US2010/0021980, US2010/0028484, US2010/0178675, US2010/0260918, US2011/0126448, US2012/0051980, US2012/0064213, US2012/0301598, US2013/0032175, US2013/0102045, US2013/0130343, US2013/0164795, WO2007/146971, WO2012036857, WO2012/125739, WO2012/145230, and WO2013033369.